Temporary vascular filter

ABSTRACT

The present invention provides a method of deploying a medical filter within a channel in a patient&#39;s body and filter systems which can be used in such a method. Such a filter may include a radially expandable body  52  having an opening  56  in a proximal length thereof. In one method, the filter is urged along a length of the channel with the filter body in a radially reduced configuration. This body is expanded to substantially fill the lumen of the vessel and orient the opening in the body proximally. Body fluid is permitted to enter the filter body through the proximally oriented opening and pass distally through the distal length of the body so that the distal length of the body filters from the body fluid particulate material entrained therein. The proximal length of the body can be drawn into the retrieval catheter, thereby effectively closing the proximally oriented opening within the catheter to retain the particulate material within the enclosure. In a preferred embodiment, the filter body  52  is formed of a porous, resilient fabric having pores therein and the proximal opening  56  is at least five times the size of such pores.

FIELD OF THE INVENTION

The present invention generally relates to filters for body passageways,and has particular utility in connection with temporary vascularfilters.

BACKGROUND OF THE INVENTION

Filters can be deployed in channels or vessels in patient's bodies in avariety of medical procedures or in treating certain conditions. Forexample, rotating burrs are used in removing atheroma from the lumen ofpatients' blood vessels. These burrs can effectively dislodge theatheroma, but the dislodged material will simply float downstream withthe flow of blood through the vessel. Filters can be used to capturesuch dislodged material before it is allowed to drift too fardownstream, possibly occluding blood flow through a more narrow vessel.

Some researchers have proposed various traps or filters for capturingthe particulate matter released or created in such procedures. However,most such filters generally have not proven to be exceptionallyeffective in actual use. These filters tend to be cumbersome to use andaccurate deployment is problematic because if they are not properlyseated in the vessel they can drift to a more distal site where they arelikely to do more harm than good. In addition, these filters aregenerally capable of only trapping relatively large thrombi and are noteffective for removing smaller embolic particles from the blood stream.

The problems with most temporary filters, which are intended to be usedonly during a particular procedure then retracted with the thrombitrapped therein, are more pronounced. Even if the trap does effectivelycapture the dislodged material, it has proven to be relatively difficultor complex to retract the trap back into the catheter through which itwas delivered without simply dumping the trapped thrombi back into theblood stream, defeating the purpose of the temporary filter device. Forthis reason, most atherectomy devices and the like tend to aspirate thepatient's blood during the procedure to remove the dislodged materialentrained therein.

One promising filter design which overcomes many of these difficultiesis shown in International Publication No. WO 96/01591 (the publicationof PCT International Application No. PCT/US95/08613), the teachings ofwhich are incorporated herein by reference. Generally, this referenceteaches a trap which can be used to filter particles from blood or otherfluid moving through a body vessel. In one illustrated embodiment, thistrap includes a basket 270 which can be deployed and retracted through acatheter or the like, making it particularly suitable for use inminimally invasive procedures such as angioplasty or atherectomyprocedures. The fact that this trap is optimally carried on a mandrel260 further enhances its utility as most common angioplasty balloons andatherectomy devices are used in conjunction with such mandrels. Whilethis trap is very useful and shows great promise in many commonprocedures, it may be possible to better retain the thrombi collected inthe filter during retrieval of the filter.

SUMMARY OF THE INVENTION

The present invention provides a method of deploying a medical filterwithin a channel in a patient's body and devices which are well suitedfor use in such procedures. In accordance with one method of theinvention, a filter and retrieval catheter are provided. This filter hasa radially expandable body having proximal and distal ends and whichdefines an enclosure. The expandable body has a distal length and aproximal length which includes an opening therein. The retrievalcatheter has a lumen with a diameter less than the maximum dimension ofthe body's expanded configuration. This filter is urged along a lengthof the channel in the patient's body with the filter body in a radiallyreduced configuration. The body is radially expanded to its expandedconfiguration such that it substantially fills the lumen of the vesseland the opening in the body is oriented proximally. Body fluid ispermitted to enter the enclosure through this proximally orientedopening and is permitted to pass through the distal length of the body.In so doing, the distal length of the body filters from the body fluidparticulate material entrained therein (assuming, of course, that thereis any such particulate material of an appropriate size). The proximallength of the body is drawn within the lumen of the catheter, therebyeffectively closing the proximally oriented opening within the retrievalsheath to retain said particulate material within the enclosure.

Further refinements of this method are envisioned. For example, in oneembodiment, the filter has a narrow proximal end which is smaller thanthe lumen of the catheter. In drawing the proximal length of the filterwithin the catheter, this narrow proximal end may be introduced into thedistal end of the catheter's lumen. The filter may then be retracteduntil the internal surface of the catheter engages the body of thefilter distally of the opening to effectively create a particulate sealtherebetween.

As noted above, the present invention also encompasses a device wellsuited for use in such procedures. In one embodiment, such a devicecomprises a collapsible filter system including a mandrel and a filter.The mandrel has proximal and distal ends and the filter is carried alongthe mandrel between these ends. The filter has a radially expandablebody having proximal and distal ends of its own. The body is formed of aporous, resilient fabric having pores therein through which a body fluidmay pass, but which are small enough to restrict passage of particulatematerial over a certain, predetermined size entrained in the body fluid.A proximally oriented hole passes through the fabric along a proximallength of the filter's body. This hole is spaced distally of theproximal end of the body and being at least about five times the size ofsaid pores.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a medical filter in accordance with oneembodiment of the present invention;

FIG. 2 is a side elevation view of the filter of FIG. 1;

FIG. 3 is a cross sectional view of the medical filter of claim 1, takenalong line 3-3 of FIG. 2;

FIG. 4 is a schematic side view in partial cross section illustrating afilter of an alternative embodiment of the invention in a radiallyreduced configuration within a catheter;

FIG. 5 is a schematic side view illustrating the filter of FIG. 4deployed in a vessel in a patient's body;

FIG. 6 is a schematic side view of the filter of FIGS. 4 and 5 withcollected particulate material trapped within the filter;

FIG. 7 is a schematic side view of the filter of FIGS. 4-6 drawn farenough into the catheter to effectively close the proximally orientedopening within the catheter; and

FIG. 8 is a schematic side view of the filter of FIGS. 4-7 withdrawncompletely within the lumen of the catheter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1-3 illustrate a filter system 10 in accordance with oneembodiment of the invention. This filter system can be used in anychannel in a patient's body, including blood vessels, the urinary tractor biliary tract and airways. This filter system 10 is optimallydesigned to be deployed in a patient's vessel in a minimally invasiveprocedure, such as by introducing the filter system into a blood vesselthrough a catheter (as described in greater detail below).

The filter system 10 of the invention generally includes a mandrel 20and a filter 50. Conceptually, the mandrel 20 can be thought of ashaving a primary function of positioning and controlling the deploymentof the filter 50 while the filter can be considered the primarytherapeutic or functional element of the system 10.

The mandrel 20 should be fairly flexible to allow the device to bedeployed in a curving body passageway without kinking or otherwiseinhibiting suitable deployment of the filter 50. While the mandrel canbe formed of any material having any dimension suitable for the task forwhich the filter system 10 is to be employed, in most circumstances, themandrel 20 will comprise an elongate metal wire. In one particularlypreferred embodiment, the mandrel 20 is formed of nitinol, a roughlystoichiometric alloy of nickel and titanium having excellent“superelastic” properties. The use of nitinol in medical guidewires andrelated applications is well known in the art and need not be discussedin detail here. If so desired, the distal-most length of the mandrel mayinclude a flexible helically wound coil 22 extending thereover. The useof such helical coils to enhance flexibility of the distal tip is wellknown in the guidewire art.

The mandrel 20 shown in FIGS. 1-3 has an enlarged diameter stop 40attached thereto. The stop 40 is spaced proximally from the distal tip25 of the mandrel 20. Desirably, the stop 40 is spaced proximally of theproximal end of the helical coil 22 of the mandrel. This permits thedistal slider 60 of the filter 50 to slide relatively freely andunencumbered along the length of the mandrel distally of the stop.

The stop 40 can be formed of any desired material and can be attached tothe mandrel 20 in any desired fashion. The stop should be attached tothe mandrel relatively securely, though, as the stop will be used tourge the filter 50 within the lumen of the vessel in which the system 10is to be deployed. As an example, the stop 40 may comprise a standardradiopaque marker band which has been securely crimped on the mandrel 20and/or attached to the mandrel using an adhesive or solder. The preciselength and shape of the stop 40 is not critical. The drawings illustratethe stop 40 as a relatively short cylindrical body attached about thecircumference of the mandrel. However, the stop 40 may have a morebulbous shape and could, in theory, even be formed integrally with themandrel.

The stop 40 effectively divides the mandrel into distal and proximallengths. The distal length 30 of the mandrel can be thought of as thatlength which extends distally from the stop 40 to the distal tip 25 ofthe mandrel. Likewise, the proximal portion 35 of the mandrel 20 can bethought of as comprising the length of the mandrel extending proximallyfrom the stop 40 to the proximal end of the mandrel.

The filter 50 shown in FIGS. 1-3 has an elongate, generally tubular body52 which extends from a distal slider 60 proximally to a proximal slider65. The body 52 of the filter can be formed of any material suitable forthe application at hand. In many applications, e.g., filtering bloodwithin a patient's vasculature, the filter body 52 typically comprises alength of a braided tubular fabric. The use of a tubular braid ofnitinol to make medical devices is described in some detail inInternational Publication No. WO 96/01591, the teachings of which wereincorporated above by reference. Briefly speaking though, this processcan employ a tubular braid of a fabric comprising two sets of nitinolwires wrapped helically about a mandrel, with one set of wires beingwrapped spirally about the mandrel in one direction and the other setbeing wrapped in the other direction. This braid is then placed incontact with a molding surface of a molding element which defines theshape of the desired functional element. By heat treating the fabric incontact with the molding surface of the molding element, one can createa functional element having virtually any desired shape.

The body 52 of the filter 50 desirably is made of a fairly flexible,resilient material. In particular, the filter 52 desirably has aradially expanded configuration, e.g., the shape shown in FIGS. 1-3,which the device will tend to resiliently assume in the absence of anycountervailing biasing force. A body 52 formed of a nitinol tubularbraid which has been heat set into the desired shape should suit thispurpose well.

In the filter system 10 shown in FIGS. 1-3, the body 52 of the filter 50assumes a generally tubular shape having tapered proximal and distalends. The maximum outer diameter of the middle length of the body 52should be sized to substantially fill the lumen of a vessel to ensurethat the filter will effectively preclude any emboli (or otherparticulate material which may be entrained in the patient'sbloodstream) from passing around the filter.

The body of the filter includes a distal length 53 and a proximal length54, each of which tapers from the middle of the body's length to theirrespective ends. In particular, the distal length 53 tapers distallytoward a narrow distal end adjacent the distal slider 60 while theproximal length 54 of the filter body tapers toward its proximal endadjacent the proximal slider 65. The rate of this tapering can be variedas desired. While FIGS. 1-3 illustrate a fairly gradual taper, thechange in diameter may be more abrupt. The filter body 52 of FIGS. 1-3is also fairly symmetrical, with the tapers of the proximal and distallengths being about the same. In some circumstances it may beadvantageous to have the two lengths taper differently, e.g. where theproximal length tapers more gradually while the distal length changesdiameter more abruptly.

The proximal length 54 of the filter body has at least one proximallyoriented opening 56 therein. This opening passes through the flexible,resilient fabric of which the body 52 desirably is formed. The fabrichas pores therein which allow fluids to pass therethrough, but the poresare small enough to prevent passage of particles larger than apredetermined size. If the body is formed of a metallic tubular braid asmentioned above, the maximum sizes of these pores can be controlled byadjusting the number of wires in the braid and the pick and pitch of thebraid. For example, if the filter 50 is to be employed as a vascularfilter, a pore size of 20-1500 microns is desirable. If such a filterbody has a maximum diameter of about 4 mm, it may be formed of 48 wireseach having a diameter of about 0.002 inches (about 50 microns) and apick rate of about 90 per inch (about 35 per centimer).

The size of the proximally oriented opening 56 should be sufficient topermit body fluid with particulate material entrained therein to enterthe enclosure within the body 52 of the filter. At a minimum, it isexpected that the opening will be at leas five times the maximum poresize of the fabric of which the body is formed, with an opening of atleast ten times the maximum pore size being preferred.

The opening 56 can be formed in any suitable fashion. If the filter isformed from a preformed flat sheet of fabric wrapped into the desiredshape, the opening can be cut through the fabric before the fabric isshaped into the filter body. If the body 52 is formed of a tubularmetallic braid, it may instead be cut through the fabric after the braidis heat set in the desired shape.

In one particularly preferred method of forming the filter (which methodcomprises another embodiment of the invention), a tubular metal braid isprovided. The distal and proximal sliders 60, 65 are attached to thebraid a suitable distance from one another. The braid is trimmed at thedistal end of the distal slider 60 and at the proximal end of theproximal slider 65. A forming mandrel (not shown) is passed between thewire strands of the braid and positioned within the tubular braid.

The forming mandrel has an external molding surface which generallycoincides with the desired shape of the filter body. The forming mandrelmay have a larger diameter than the inner diameter of the tubular braidand the braid may be drawn down against the forming mandrel by applyingaxial tension to the braid. This structure may be heated at an elevatedtemperature to heat-set the filter body 52 in this shape and the formingmandrel may be removed.

The forming mandrel includes a proximal projection having a peripherythe size and shape of the desired proximal opening 56. This projectionextends through the wire mesh of the tubular braid during heattreatment, forcing the wire strands to extend about the periphery of theprojection. As a consequence of the heat treatment, when the formingmandrel is removed, the wires will retain the proximal opening withoutrequiring cutting the fabric.

In FIGS. 1-3, the filter 50 is shown as having a single opening 56extending over only one side of the proximal length 54 of the filterbody (i.e., above the mandrel 20 in FIG. 2). To increase the percentageof body fluid which passes into the enclosure of the filter body, thenumber of openings or the shape of the opening(s) can be adjusted tomaximize the cross sectional area of the vessel covered by the openings.For example, a plurality of openings can be spaced equiangularly aboutthe proximal length 54, such as three openings arranged about 120degrees from one another.

The opening 56 in FIGS. 1-3 is generally elliptical with a major axisextending generally in a plane which contains the axis of the mandrel20. If one were to increase coverage of the opening 56 by adjusting itsshape, the strength of the filter and its connection to the proximalslider 65 should not be compromised. One way to accomplish this is tooffset the filter 50 with respect to the mandrel 20. In FIGS. 1-3, thebody 52 of the filter is generally symmetrical about a centrallongitudinal axis and this axis generally coincides with the axis of themandrel. One could instead make the filter asymmetrical, with the axisof the mandrel 20 spaced radially outwardly from the central axis of thebody 52. In such a design, the mandrel could extend adjacent to one sideof the body and the opposite side of the body would extend farther fromthe mandrel. By positioning the opening 56 on the larger side of thebody, the opening can be made larger and cover more of the crosssectional area of the vessel in which the filter is deployed.

While the opening 56 can extend up to or even into the proximal slider65, in a preferred embodiment the opening 56 is spaced distally from theslider 65 and the proximal end of the body 52. This will enable a moresecure connection between the slider 65 and the body. The distal end ofthe opening desirably terminates proximally of the location where thefilter body has its maximum diameter. This will minimize the chance thatbody fluid could slip between the filter and the wall of the vessel inwhich the filter is deployed. This will also provide a more effectiveseal between the filter body 52 and the catheter in which it isretrieved. (Such retrieval is discussed below in connection with FIGS. 7and 8.)

The filter 50 is attached to or carried by the mandrel 20 by means of aproximal slider 65 attached to the body 52 adjacent its proximal end anda distal slider 60 attached adjacent the distal end of the body 52. Thedistal slider 60 should be free to slide along at least a proximalportion of the distal length 30 of the mandrel while the proximal slider65 should be free to slide along at least a distal portion of theproximal length 35 of the mandrel. In use, the stop 40 of the mandreleffectively defines a limit on the range of motion of these sliders 60,65.

While each of the sliders 60, 65 should be slidable along its respectivelength of the mandrel, the sliders can take any desired shape. In theillustrated embodiments, each slider comprises a relatively thin ringwhich is carried about the mandrel. The thin ring can be attached to thebody 52 in any desired fashion, such as by crimping or swaging thefabric of the body between two layers of the ring or soldering, weldingor otherwise adhering the fabric to the ring.

The stop 40 of the mandrel is positioned within the body 52 of thefilter and is not exerting any biasing force on either of the sliders60, 65. In this configuration, the mandrel 20 can be moved proximallyand distally with respect to the filter 50 without substantiallyaffecting the shape or position of the filter. The limits of this rangeof free movement of the mandrel with respect to the filter are generallydefined by the relationship between the stop 40 and the sliders 60, 65.In particular, the mandrel can be moved from a distal position whereinthe stop 40 abuts but does not exert any force on the distal slider 60and a proximal position wherein the stop 40 abuts, but does not exertany significant force on, the proximal slider 65. This allows the filter50 (or any other functional element which is carried by the mandrel) tobe fairly precisely positioned within a patient's vessel and retain thatposition even if the guidewire is moved slightly during use. This can beadvantageous in circumstances where other devices are exchanged over theguidewire (e.g., during angioplasty and atherectomy procedures).

The inner diameter of the generally annular collars defining the sliders60, 65 is desirably larger than the outer diameter of the mandrel, butshould be smaller than the outer diameter of the stop 40. In thisfashion, the stop serves as an effective limit on proximal movement ofthe distal slider 60 and distal movement of the proximal slider 65.Apart from this relationship with the slider 40 and the fact that bothsliders are indirectly linked to one another by the body 52 of thefilter, the proximal and distal sliders are slidable along the mandrelessentially independently of one another.

When the mandrel 20 is urged distally (to the left in FIGS. 2 and 3)against the distal slider 60, the stop will exert a distal biasing forceagainst the distal end of the body 52 of the filter. In theory, if thefilter were used in a frictionless environment, the filter would travelwith the mandrel without any appreciable alteration in the shape of thebody 52. In most clinical applications, though, this is not the case.Instead, there is typically some force restraining completely freemovement of the filter within the channel of the patient's body.Typically (and as suggested in FIGS. 5 and 6, for example), the body 52of the filter will resiliently expand into physical contact with theinterior surface of the vessel within which it is deployed. This contactwith the vessel wall will tend to hold the filter 50 in place as thestop of the mandrel slides proximally and distally between the twosliders 60, 65. When the mandrel is urged distally until it exerts adistal force against the distal slider 60, this force will tend toaxially elongate the body 52.

Resilient tubular braids tend to assume a radially reduced profile uponaxial elongation. (This property and some of its implications arediscussed in International Publication No. WO 96/01591, mentionedpreviously.) As a consequence, when the mandrel 20 is urged distally topush distally against the distal slider 60, this distal force actsagainst the restorative force of the resilient braid, which wouldotherwise bias the braid into its expanded configuration (FIGS. 1-3). Byovercoming this restorative force with a countervailing distal force,the body 52 will tend to both axially elongate and assume a radiallyreduced profile. This, in turn, reduces the force with which the bodyengages the wall of the vessel or catheter in which the filter ispositioned and reduces friction between the filter 50 and the vessel orcatheter. Hence, urging the mandrel distally to move the filter 50distally will, at the same time, reduce friction between the filter andthe vessel wall to further facilitate advancement of the filter alongthe vessel's lumen. This requires less force to push the filterdistally, enabling the mandrel to be smaller and reducing the outerdiameter of the collapsed device, making deployment in smaller vesselsfeasible. In addition, the reduced friction between the filter and thevessel wall limits damage to the intima of the vessel, permitting thefilter to be deployed and moved with a minimum of trauma.

When the mandrel is retracted proximally, the stop 40 of the mandrelwill abut against, and exert a proximal biasing force on, the proximalslider 65 of the filter 50. This proximal biasing force will act againstthe restorative force of the body 52 to axially elongate and radiallyreduce that body. This permits the device to be withdrawn proximallyalong the lumen of the vessel either for repositioning at a moreproximal location or for withdrawal from the patient's body at the endof the procedure.

In the embodiment of FIGS. 1-3, the proximal and distal sliders 60, 65are free to move relatively independently of one another, limitedprimarily by their indirect link to one another through the body 52 ofthe filter. For example, when the mandrel 20 is urged distally againstthe distal slider 60 (FIG. 4), the proximal slider will slide proximallyalong the proximal length 35 of the mandrel. Similarly, when the mandrelis withdrawn proximally to urge proximally against the proximal slider65, the distal slider will be free to drift distally along the distallength 30 of the mandrel. Ideally, there should be a sufficient distancebetween the distal shoulder of the stop 40 and the proximal end of thehelical coil 22 at the distal end of the mandrel.

FIGS. 4-8 schematically depict one method of the invention utilizing analternative filter design. Most of the elements of the filter 50′ inFIGS. 4-8 are essentially the same as like elements in FIGS. 1-3, so thesame reference numbers have been used for most elements in both sets ofdrawings. The primary differences between the filter 50′ of FIGS. 4-8and the filter 50 described above is that the stop 40 has been omittedin FIGS. 4-8 and the proximal slider 65′ has been secured to the mandrel20 at a fixed location. The distal slider 60 remains free to slide alongthe mandrel.

The body 52′ of the filter 50′ is shaped a little differently from thefilter body 52 of FIGS. 1-3. This difference is not crucial and does notyield significantly different properties. Instead, the differences inthe fully deployed shapes of the two filters 50, 50′ are intended tohighlight that the shape can vary without compromising the filter'sfunction.

FIG. 4 schematically illustrates the filter 50′ collapsed within thelumen of a catheter C. The body 52′ of the filter has been collapsedunder the biasing force of the catheter walls into an axially elongated,radially reduced configuration. This catheter and filter combination maybe advanced through a patient's body as a unit until a specifictreatment site has been reached, but this combined unit may be dificultto steer through a more tortuous path. For many applications (e.g.,deployment at a remote site within a patient's vasculature), thecatheter will first be positioned adjacent the treatment site. Only thenwill the filter system be inroduced into the distal end of the catheterC and urged along the catheter's lumen and the vessel V until the distalend 25 of the mandrel and the distal slider 65 are positioned adjacentthe distal end of the catheter, as shown in FIG. 4.

Regardless of how the system reaches the state illustrated in FIG. 4,once the catheter is in place the filter 50′ can be deployed out thedistal end of the catheter. In particular, the filter 50′ may be urgedout of the distal end of the catheter, e.g., by holding the catheter Cstill and urging the mandrel 20 distally or by holding the mandrel 20stationary and withdrawing the catheter C proximally.

Upon exiting the distal end of the catheter C, the flexible body 52 willresiliently expand radially outwardly, desirably until it engages thewall of the vessel V or, less desirably, is positioned adjacent to thevessel wall. (Such a configuration is shown in FIG. 5.) This will helpensure that all fluid passing along the vessel V will have to passthrough the filter body 52′.

A substantial portion (ideally, all or at least a vast majority) of thebody fluid in the vessel should pass through the proximally orientedopening 56 in the filter body. Since the opening is fairly large, it isanticipated that any particulate material entrained in the body fluidtravelling through the vessel will enter the interior of the filterthrough the opening 56. The pores in the distal length 53 of the filterbody are significantly smaller, though, so most oversized particles willbe trapped within the enclosure of the filter body. FIG. 6 schematicallydepicts such a situation, with a number of individual particles P beingshown trapped within the filter body. If the filter 50 or 50′ is to beused in a vascular procedure, the pores should be large enough to permitred blood cells to pass therethrough, but small enough to trap thrombior emboli above a certain predetermined size.

A wide variety of vascular filters are known in the art and the easewith which such filters can be deployed varies. One of the primarydistinguishing characteristics between these various filter designs isthe ease with which the filters can be withdrawn from or repositionedwithin the patient's body. For example, most commercially available venacava filters are provided with sharp barbs or other structures whichfirmly seat the devices in a wall of the vessel, but which effectivelypreclude retraction of the device. Temporary filters avoid suchtenacious attachments to the vessel wall, permitting them to beretracted or moved after initial deployment. As noted above, though, oneof the primary difficulties encountered in using such temporary filtersis the risk of dumping the captured particulate material back into thevessel from which it was filtered. Many designs require that thephysician first aspirate the particulate material or, in the case ofthrombi captured in vascular procedures, use drugs which help break downthe particles to clinically acceptable sizes.

International Publication No. WO 96/01591, mentioned previously,provides a particularly useful filter. This filter, which may begenerally dome-shaped and have a proximally-facing lip, enables aphysician to close the filter prior to retraction, keeping the capturedparticles within the filter during removal or repositioning.Unfortunately, this design is mechanically complex. In one embodimentdisclosed therein, the filter is provided with a drawstring which can beused to draw the proximal edge of the filter down toward the wire onwhich it is carried, minimizing the risk of losing the particles. Asecond design proposed in this reference employs a separately deployablecover which can be brought into sealing engagement with the filter.While this may further reduce the risk of dumping particles back intothe vessel, the increased mechanical complexity makes it difficult toprovide a highly reliable, cost-effective device.

The present invention provides an elegant solution to these difficultieswhich minimizes mechanical complexity and promises to provide veryeffective containment of filtered particles. FIG. 7 shows the filter 50′of FIGS. 4-6 partially retracted into the catheter C. If the filter isbeing used for only a short period of time, the catheter C may be thesame catheter used to initially deploy the filter in the vessel. If thefilter is to be left in place for a longer period of time, though, itmay be preferred to remove the deployment catheter (FIG. 4) from thepatient's body and later introduce a separate retrieval catheter byadvancing the retrieval catheter along the mandrel 20.

The lumen of the retrieval catheter C in FIG. 7 has a diameter smallerthan the maximum cross-sectional dimension of the body's expandedconfiguration. The lumen is larger than the narrow proximal end of thefilter body 52′ adjacent the proximal slider 65′, though, and theillustrated filter body is spaced from the vessel wall about its entireperiphery. As a consequence, the distal tip of the catheter can bepositioned between the proximal end of the body 52′ and the wall of thevessel V before the catheter engages the body of the filter adjacent theslider. This can be done by holding the catheter in place andwithdrawing the mandrel proximally, by holding the mandrel stationaryand moving the catheter distally, or moving both the catheter and themandrel.

Once the proximal end of the body 52′ is introduced into the catheter'slumen, the rest of the body can be drawn into the lumen of the catheter.Again, the body can be drawn into the catheter by advancing the catheterdistally or retracing the filter proximally. At some point, the wall ofthe catheter C will engage the larger diameter body 52. Ideally, thelumen of the catheter is notably smaller than the deployed diameter ofthe filter body. As shown in FIG. 7, in this case the walls of thecatheter will exert a biasing force to urge the body toward the radiallyreduced configuration in which it was initially deployed (FIG. 4).

Perhaps more importantly, though, the internal surface of the catheterengages the body of the filter distally of the filter's proximallyoriented opening 56. While the opening may still be open to the lumen ofthe catheter, the engagement between the filer body and the catheterwall distally of the opening effectively creates a particulate sealtherebetween. As a consequence, simply by advancing the catheter C withrespect to the filter 50′, one can seal within the combined catheter andfilter all of the captured particles above the predetermined minimumsize. This combination can then be moved as a unit either to remove itfrom or reposition it within the patient's body with minimal risk oflosing any of the captured particles.

If the filter is to be completely withdrawn from the vessel, it ispreferred that the filter body 52′ be completely withdrawn into thelumen of the catheter (as shown in FIG. 8) rather than leaving a distalsection of the filter extending out of the catheter (as shown in FIG.7). This will reduce friction against the vessel wall, making withdrawaleasier and reducing trauma to the intima of the vessel.

While a preferred embodiment of the present invention has beendescribed, it should be understood that various changes, adaptations andmodifications may be made therein without departing from the spirit ofthe invention and the scope of the appended claims.

1. A method of deploying a medical filter within a channel in a patient,the method comprising: a) providing a filter having a radiallyexpandable body having proximal and distal ends, the proximal endconnected to a proximal element and the distal end connected to a distalelement, the proximal and distal elements being ring shaped and sized toreceive an elongate member in a configuration such that the proximal anddistal elements are spaced apart along a longitudinal length of theelongate member, the filter defining an enclosure, the body having adistal length and a proximal length, the body being formed of a porous,resilient fabric comprising strands spaced apart to define poresextending through the fabric through which a body fluid may pass, butwhich restrict passage therethrough of particulate material entrained inthe fluid, the body having at least one proximally oriented openingformed between strands of the fabric, the strands having been spacedapart such that the at least one opening is at least ten times the sizeof the pores, the at least one opening passing through the fabric alongthe proximal length of the body, and a retrieval catheter having a lumenwith a diameter less than a maximum dimension of the body's expandedconfiguration; b) urging the filter along a length of the channel withthe filter body in a radially reduced configuration; c) radiallyexpanding the body to its expanded configuration such that itsubstantially fills the lumen of the channel and the opening in the bodyis oriented proximally; d) permitting fluid to enter the enclosurethrough the proximally oriented opening and pass distally through thedistal length of the body, the distal length of the body filtering fromthe fluid particulate material entrained therein; and e) drawing theproximal length of the body within the lumen of the retrieval catheter,thereby effectively closing the proximally oriented opening within thecatheter to retain the particulate material within the enclosure.
 2. Themethod of claim 1 wherein the proximal length of the filter's bodytapers proximally to a narrow proximal end which is smaller than thelumen of the catheter, the step of drawing the proximal length withinthe catheter comprising receiving the narrow proximal end of the body inthe lumen of the catheter then retracting the filter until the internalsurface of the catheter engages the body of the filter distally of theopening to effectively create a particulate seal therebetween.
 3. Themethod of claim 2 wherein the narrow proximal end of the body is spacedfrom a wall of the channel when the filter is expanded into its expandedconfiguration.
 4. The method of claim 3 wherein a wall of the catheteris positioned between the narrow proximal end of the body and the wallof the channel as the proximal length of the body is drawn into thelumen of the catheter.
 5. The method of claim 1 wherein a wall of thecatheter urges the filter's body radially inwardly toward the radiallyreduced configuration as the body is drawn into the lumen thereof. 6.The method of claim 1 wherein the filter is urged along the channel inthe radially reduced configuration within a deployment catheter.
 7. Themethod of claim 6 wherein the same catheter is used as both thedeployment catheter and the retrieval catheter.
 8. The method of claim 6wherein the deployment catheter's wall constrains the filter body in theradially reduced configuration when the body is received in the lumenthereof, the body being radially expanded by deploying the filter out ofthe distal end of the catheter, whereupon the body resiliently expandsradially outwardly upon removal of the constraint.
 9. The method ofclaim 1 wherein the retrieval catheter is held substantially stationaryas the proximal length of the filter's body is drawn therewithin. 10.The method of claim 1 wherein the proximal length of the filter's bodyis drawn into the catheter's lumen by holding the body substantiallystationary and advancing the catheter distally over the proximal lengththereof.
 11. The method of claim 1 wherein the filter is carried by amandrel, the catheter being advanced along the mandrel prior to drawingthe body of the filter into the lumen thereof.
 12. The method of claim 1wherein the elongate member is a guidewire.
 13. A method of making amedical filter body comprising: providing a tubular metal braid havingdistal and proximal ends, the braid being formed from wire strands;passing a forming mandrel between wire strands of the braid between thedistal and proximal ends of the tubular braid to force the wire strandsapart such that they extend about a periphery of the forming mandrel;heating the tubular metal braid to a temperature sufficient to heat setthe wire strands extended about the periphery of the forming mandrelsuch that an opening in the shape of the periphery of the formingmandrel is formed in the metal braid; and removing the forming mandrelfrom the tubular braid.
 14. The method of claim 13 wherein the distaland proximal ends of the tubular metal braid are tapered.
 15. The methodof claim 13 wherein the forming mandrel has an external molding surfaceand wherein the method further comprises applying axial tension to thebraid to draw the braid down against the molding surface of the formingmandrel.
 16. The method of claim 13 wherein the forming mandrel has anexternal molding surface with a diameter greater than a diameter of thetubular braid and wherein the method further comprises applying axialtension to the braid to draw the braid down against the molding surfaceof the forming mandrel.
 17. The method of claim 13 wherein the formingmandrel has an external molding surface having a diameter greater than adiameter of the tubular braid and wherein during the step of passing theforming mandrel between wire strands of the braid the diameter of thebraid increases.
 18. The method of claim 17 further comprising: applyingaxial tension to the braid to draw the braid down against the externalmolding surface of the forming mandrel.
 19. A method of making a medicalfilter comprising: providing a tubular metal braid formed of wirestrands; attaching distal and proximal elements to the braid spaced fromone another to form a filter body between the proximal and distalelements, the filter body having a proximal portion extending betweenthe proximal element and a midpoint of the filter body; passing aforming mandrel between wire strands of the proximal portion of thebraid to force the wire strands to extend about a periphery of theforming mandrel; heating the tubular metal braid to a temperaturesufficient to heat set the wire strands extended about the periphery ofthe forming mandrel to form a proximal opening in the filter body; andremoving the forming mandrel.
 20. The method of claim 19 wherein theforming mandrel has an external molding surface and wherein the methodfurther comprises applying axial tension to the braid to draw the braiddown against the external molding surface of the forming mandrel. 21.The method of claim 19 wherein the forming mandrel has an externalmolding surface with a diameter greater than a diameter of the tubularbraid and wherein the method further comprises applying axial tension tothe braid to draw the braid down against the external molding surface ofthe forming mandrel.
 22. The method of claim 19 wherein the formingmandrel has an external molding surface having a diameter greater than adiameter of the tubular braid and wherein during the step of passing theforming mandrel between wire strands of the braid the diameter of thebraid increases.
 23. The method of claim 19 further comprising: applyingaxial tension to the braid to draw the braid down against the formingmandrel.
 24. The method of claim 19 further comprising: trimming thebraid at a distal end of the distal element and at a proximal end of theproximal element.
 25. The method of claim 19 wherein the forming mandrelhas an external molding surface with a periphery that generallycoincides with a desired shape of the opening in the filter body.
 26. Amethod of making an opening in the tubular body of a medical filterformed from braided wire strands, the tubular body having distal andproximal ends, the method comprising: passing a forming mandrel betweenwire strands of the braid between the distal and proximal ends of thetubular body to force the wire strands apart such that they extend abouta periphery of the forming mandrel; heating the tubular body to atemperature sufficient to heat set the wire strands extended about theperiphery of the forming mandrel such that an opening in the shape ofthe periphery of the forming mandrel is formed in the tubular body ofthe medical filter; and removing the forming mandrel from the tubularbody.
 27. Apparatus for filtering emboli from blood flowing through avessel, the apparatus comprising: a guide wire having a distal regionand a stop on the distal region; a capture ring disposed for translationon the guide wire, the stop limiting translation of the capture ring ina distal direction; and a filter sac connected to the capture ring. 28.The apparatus of claim 27 wherein, when the filter sac is deployed inthe vessel, rotation or distal translation of the guide wire relative tothe capture ring does not displace the filter sac, but retraction of theguide wire in a proximal direction causes the stop to abut against thecapture ring.
 29. Apparatus for filtering emboli from blood flowingthrough a vessel, the apparatus comprising: a guide wire having a firstportion having a first diameter and a distal region having a seconddiameter greater than the first diameter; and a filter element having acapture ring disposed for translation on the first portion, the capturering having an aperture greater than the first diameter but smaller thanthe second diameter, wherein rotation or distal translation of the guidewire relative to the capture ring does not displace the filter element.30. The apparatus of claim 29 wherein the filter element comprises anexpandable sac.
 31. The apparatus of claim 29 wherein the guide wirefurther comprises a flange disposed on the distal region having adiameter larger than the diameter of the aperture in the capture ring.32. The apparatus of claim 29 wherein the filter element has acontracted state suitable for transluminal delivery, and the distalregion has a length that is greater than a length of the filter elementin the contracted state.
 33. Apparatus for filtering emboli duringtreatment of occlusive disease in a vessel, the apparatus comprising: aguide wire having a first diameter and a distal region having a seconddiameter greater than the first diameter; a filter element having a saccoupled to a capture ring, the capture ring having an aperture greaterthan the first diameter but smaller than the second diameter, whereinthe filter element is disposed on the guide wire and the guide wireextends through the aperture with the distal region disposed distally ofthe capture ring, so that when the filter element is deployed in thevessel, rotation or distal translation of the guide wire does notdisplace the filter element, but retraction of the guide wire in aproximal direction causes the distal region to abut against the capturering.
 34. A method of filtering emboli from blood flowing through avessel, the method comprising: providing a guide wire having a distalregion including a stop, and a filter element having a capture ringdisposed for translation on the guide wire proximal of the stop;transluminally inserting the guide wire and filter element into avessel; deploying the filter element to engage a wall of the vessel, thefilter element filtering emboli out of blood flowing through the vessel;and advancing a treatment device along the guide wire to treat a portionof the vessel proximal to the location of the filter element, rotationor distal translation of the guide wire relative to the filter elementimparted by the treatment device not displacing the filter element. 35.The method of claim 34 further comprising a step of, after use of thetreatment device is completed, pulling the guide wire proximally so thatthe stop engages the capture ring and causes the filter element toreturn to the contracted state.
 36. The method of claim 34 furthercomprising: providing a delivery sheath; and compressing the filterelement to a contracted state to insert the filter element within thedelivery sheath.
 37. The method of claim 34 wherein the filter elementcomprises an expandable sac, and deploying the filter element comprisesexpanding the expandable sac so that a perimeter of the expandable saccontacts the wall of the vessel.
 38. The method of claim 37 wherein thefilter element further comprises a cylindrical sleeve and deploying thefilter element further comprises expanding the cylindrical sleeveagainst the wall of the vessel.
 39. The method of claim 34 furthercomprising providing a catheter having a lumen, and pulling the guidewire proximally causes the filter element to become retracted within thelumen.
 40. Apparatus for filtering emboli from blood flowing through avessel, the apparatus comprising: a mandrel having a distal end and astop spaced proximally of the distal end; a slider disposed fortranslation on the mandrel, the stop limiting translation of the sliderin a distal direction; and a vascular filter connected to the slider.41. The apparatus of claim 40 wherein, when the vascular filter isdeployed in the vessel, rotation or distal translation of the mandrelrelative to the slider does not displace the vascular filter, butretraction of the mandrel in a proximal direction causes the stop toabut against the slider.
 42. Apparatus for filtering emboli from bloodflowing through a vessel, the apparatus comprising: a mandrel having adistal end and a proximal length having a first diameter and a stopspaced proximally of the distal end having a second diameter greaterthan the first diameter; and a filter element having a slider disposedfor translation on the proximal length, the slider having an aperturegreater than the first diameter but smaller than the second diameter,wherein rotation or distal translation of the mandrel relative to theslider does not displace the filter element.
 43. The apparatus of claim42 wherein the filter element comprises an expandable vascular filter.44. Apparatus for filtering emboli during treatment of occlusive diseasein a vessel, the apparatus comprising: a mandrel having a distal end anda proximal length having a first diameter and a stop spaced proximallyof the distal end, the stop having a second diameter greater than thefirst diameter; a filter element having a vascular filter coupled to aslider, the slider having an aperture greater than the first diameterbut smaller than the second diameter, wherein the filter element isdisposed on the mandrel and the mandrel extends through the aperturewith the stop disposed distally of the slider, so that when the filterelement is deployed in the vessel, rotation or distal translation of themandrel does not displace the filter element, but retraction of themandrel in a proximal direction causes the stop to abut against theslider.
 45. A method of filtering emboli from blood flowing through avessel, the method comprising: providing a mandrel having a distalregion including a stop, and a filter element having a slider disposedfor translation on the mandrel proximal of the stop; transluminallyinserting the mandrel and filter element into a vessel; deploying thefilter element to engage a wall of the vessel, the filter elementfiltering emboli out of blood flowing through the vessel; and advancinga treatment device along the mandrel to treat a portion of the vesselproximal to the location of the filter element, rotation or distaltranslation of the mandrel relative to the filter element imparted bythe treatment device not displacing the filter element.
 46. The methodof claim 45 further comprising a step of, after use of the treatmentdevice is completed, pulling the mandrel proximally so that the stopengages the slider and causes the filter element to return to thecontracted state.
 47. The method of claim 45 further comprising:providing a catheter having a lumen; and compressing the filter elementto a contracted state to insert the filter element within the lumen ofthe catheter.
 48. The method of claim 45 wherein the filter elementcomprises an expandable vascular filter, and deploying the filterelement comprises expanding the expandable vascular filter so that aperimeter of the expandable vascular filter contacts the wall of thevessel.
 49. The method of claim 45 further comprising providing acatheter having a lumen, and pulling the mandrel proximally causes thefilter element to become retracted within the lumen.